Unfortunately, I didn't get a chance to test out how well the game worked in its ideal environment: With two players cooperatively tackling the campaign. Apparently, the likelihood of corralling two people with two PSPs and two copies of the game is about as low as corralling one unicorn.
Army of Two: The 40th Day for PSP succeeds at everything it tries to do. It's added a level of complexity to the point-at-things-to-kill-them recipe the twin-stick genre is known for by adding a basic cover mechanic and aggro management to the equation.
The latter is handled by changing your partner between passive and aggressive mode, which either lets you take the brunt of the attack, or lets you lose enemy attention, allowing you to flank them. For some of the heavily armored enemies, these tactics must be adopted to survive. As the PSP's pathetic analog nub lacks a partner on the handheld, the actual gunplay is controlled by the face buttons, each of which fire in the appropriate direction (with a bit of forgiving lock-on support, to boot).
Completing objectives earns you cash, which you either spend on new weapons or upgrading the ones you've already got. While there aren't a ton of armaments in the game -- certainly not as many as the build-a-gun workshop provided in the core console title -- this added another interesting layer of strategy.
Unfortunately, after a few hours, I felt like I'd seen everything there was to see from the PSP version of The 40th Day. Enemy variation is extremely limited, the levels are completely linear, and the number of helicopters and gunships you face off against rivals that of 50 Cent: Blood on the Sand. The whole thing just feels like it's on rails, especially since most levels include a lengthy segment where you stave off waves of enemies while riding ... on rails.
The storytelling isn't exactly gripping, either. Rios and Salem, both of which are fully voiced, frequently exchange hyper-manly quips about how hard it is to be a mercenary. Sadly, the first installment in the Army of Two franchise taught us that men don't bond with their words. They bond with their fists. Due to the PSPs limited smattering of buttons, there's sadly no interface for that exchange.
Speaking of the voice work, the game's highlight comes in the form of Salem and Rios' coordinator: the tough-as-nails Alice Murray, who -- no joke -- screams every single line she delivers. It's as though she's trying to communicate with someone at a noisy concert, and it never stops being unintentionally hilarious.
The fact is, if this had been a $15 XBLA or PSN game, I'd have no problem recommending it. But for $40, it's just not worth it -- especially on the PSP, where a local-only multiplayer option almost ensures that the cooperative experience the game was designed around will never get utilized. It's a shame, really.
Or, as Alice would say, IT'S A SHAME, REALLY!